When certain halogenated pyrimidines such as bromodeoxyuridine (BrdUrd) and iododeoxyuridine (IdUrd) are incorporated into cellular DNA, cells become more sensitive to ionizing radiation and chemotherapy drugs. IdUrd tumor DNA replacement data has been obtained from a number of patients (head/neck, sarcoma tumors) receiving IdUrd and has thus far revealed replacement values ranging from 7.3 to 14.2%, much higher than was seen for gliomas. When multiple biopsies are taken from patients with head and neck tumors receiving IdUrd continuous infusion, it was observed that IdUrd DNA replacement reached maximum values after 5-7 days infusion. These findings have led to a change in the clinical protocol where IdUrd will be infused for 5 days followed by a 2-3 day break. This approach will hopefully lead to significant tumor radiosensitization and lessen normal tissue sensitization. Ultimately we wish to determine if a correlation exists between IdUrd replacement and treatment outcome. Additionally, a new clinical protocol involving IdUrd combined with low dose rate irradiation in the treatment of cervix cancer has been initiated. Biopsies will be taken prior to, during, and after irradiation to determine IdUrd incorporation, labelling index, and the potential doubling time of the tumor. These parameters will be compared/contrasted with the clinical response. Laboratory studies suggest that the higher the IdUrd replacement, the greater the extent of radiosensitization. We will provide data to directly test this hypothesis in humans.